1. Field of the Invention
The present invention relates to an inkjet printing apparatus configured to print on a print sheet by ejecting ink from an inkjet head.
2. Description of the Related Art
Generally, inkjet printing apparatuses using the inkjet method are capable of not only printing images, characters, and the like by ejecting ink from nozzles of inkjet heads to print sheets on the basis of print data such as image information and character information, but also of printing the print data on print sheets in colors by use of multiple color inks. Such inkjet printing apparatuses have been widely spread for home and office use.
A well-known example of this type of inkjet printing apparatuses is a line-type inkjet printing apparatus. This inkjet printing apparatus uses multiple inkjet heads in each of which multiple nozzles are arranged in lines extending in a main scanning direction. Thus, the inkjet printing apparatus is capable of printing at least one whole line of print data on a print sheet at once by conveying the print sheet in a sub-scanning direction orthogonal to the main scanning direction, relative to the multiple inkjet heads.
The inks used for such an inkjet printing apparatus have temperature characteristics that their viscosities vary depending on a temperature condition in a way that the viscosities become higher as the temperature decreases and the viscosities become lower as the temperature increases. Particularly in the case where the viscosities of the inks become higher, it is likely that no high-precision printed sheets may be obtained because the droplet diameter and ejection speed of ink droplets become uneven.
With this taken into consideration, Japanese Unexamined Patent Application Publication No. 2004-322411 proposes an image recording apparatus in which: an ink passage is formed in the inside of each of the ink tanks, recording heads, and supply lines; a hot water passage through which to circulate hot water is installed in a vicinity of at least part of each ink passage; temperature sensors configured to sense the temperature of ink in each ink passage are installed in at least two places in the ink passage; and at least one of the temperature and flow rate of the hot water to be circulated through the corresponding hot water passage is controlled depending on the temperature difference between the temperatures sensed by the temperature sensors.